Two-stage supercharger



Aug. 29, 1939. w. A. PARKINS I TWO-STAGE SUPERCHARGER Filed March- 26, 19s? 4 Sheet-Sheet 1 IN V EN TOR.

. Wriglz/A P9112275 f M ATTORNEY Aug. 29, 1939. w. A. PARKINS TWO-STAGE SUPERCHARGER Filed March 26, 1937 4 Sheets-Sheet 2 V INVENTOR. I/WlqlzfAParhbs A TTORNEY Filed March 26, 1937 4 Sheets-Sheet 3 1| INVENTOR.

WrzgbfAParkzhs A TTORNEY Aug. 29, 1939. w. A. PARKING TWO-STAGE SUPERCHARGER 4 Sheets-Sheet 4 Filed March 26, 1937 I N V EN TOR. PWjglziA.PHi1s7h5 A TTORNEY Patented Aug. 29, 1939 TWO-STAGE SUPERCHARGER.

Wright A. Parkins, West Hartford, Conn., as-

signor to United Aircraft Corporation, East Hartford, 001111., a corporation of Delaware Application March 26,

Claims.

'This invention relates to improvement in superchargers for internal combustion engines and has particular reference to multistage superchargers for use with engines adapted to operate at exces- 5 sively high altitudes or under low atmospheric pressure conditions.

An object of the invention resides in the provision of an improved control mechanism for a multi-stage supercharger of the character indicated.

A further object resides in the provision in combination with a multi-stage supercharger of the character indicated of an improved control means for maintaining the air pressure at the intake of the engine carburetor substantially constant over a wide rang of variation in the pressure of the external atmosphere.

. A still further object resides in the provision of improved control means which will automatically control the supercharger stages to maintain the pressure of the carburetor intake air substantially constant regardless of variation in the pressure of the external atmosphere up to the limit of the capacity of the supercharger.

Other objects and advantages will be particularly pointed out hereinafter or will become apparent as the description proceeds. In the accompanying drawings in which like reference numerals are used to designate similar parts throughout, there is illustrated a suitable mechanical embodiment of what is'now considered to be a preferred form of the idea of the invention. The drawings, however, are for the purpose of illustration only and are not to be taken as limiting the invention, the scope of which is to be measured entirely by the scope of the appended claims.

In the drawings, Fig. 1 is a side elevational view of an internal combustion engine, such as a radial air-cooled engine ordinarily utilized for the propulsion of airplanes, provided with a multi-stage supercharger and a control arrangement therefor constructed according to the idea of the invention.

Fig. 2 is a rear view of the engine and supercharger arrangement illustrated in Fig. 1, portions of the engine being omitted for the sake of clearness in the illustration.

Fig. 3 is an elevational view of one of the air a portion thereof being broken away to illustrate the construction of an automatic relief valve used in combination with other elements of the invention.

ducts connecting the various supercharger stages,

Fig. 4 is a schematic illustration of the opera- 1937, Serial No. 133,160

' tion of the control mechanism illustrated in Figs. 1 and 2.

Fig. 5 is a schematic sectional view of a two stage supercharger showing the application thereto of a control device constructed according to the invention.

Referring to the drawings in detail and particularly to Fig. 1, there is illustrated an internal combustion engine of a type ordinarily employed for the propulsion of aircraft and well known to the art. This engine comprises in general a crankcase I0 upon which are mounted one or more rows or banks of cylinders l2 extending radially outward from the crankcase. A crankshaft extends through the center of the crankcase and is connected in the usual manner to pistons operative in the cylinders 12. At its front end, the crankshaft, or a drive shaft connected therewith by suitable gears or otherwise, projects through the-nose piece [4 of the engine and is provided with splines l8 for the reception of an aeronautical propeller, not illustrated.

At its rear end the crank shaft I6 is operatively connected to the drive of a supercharger, generally indicated at 20, for supplying, in combination with the carburetor, generally indicated at 22, combustible mixture to thecylinders l2 at a pressure adequate to maintain the rated horsepower of the engine over a wide range of variations of the pressure of the external atmosphere.

The drive from the crankshaft may extend through the supercharger and operate a group of accessories, generally indicated at 24, mounted upon the rear of the engine and including such devices as magnetos, oil pumps, tachometers, gun synchronizers, and other necessary or desirable devices.

' In the form of the invention illustrated, the engine is provided with a two stage supercharger having one rotary compressor 26, hereinafter referred to as the primary stage, for initially compressing the air withdrawn from the surrounding atmosphere, and a second rotary compressor 2B, hereinafter referred'as the secondary stage, for further compressing the air and delivering the same to the engine cylinders. The carburetor 22 is pneumatically'disposed between the primary and secondary stages of the supercharger.

In the arrangement illustrated, the air is drawn into the primary supercharger stage from the surrounding atmosphere through the scoop or duct 30. It is compressed in the primary stage and passed from the primary stage through the ducts 32 and intercoolers 34 to the carburetor 22 where fuel is'added to the air to provide a combustible mixture. From the carburetor the fuel mixture is led through the duct 36 to the secondary compressor stagfi. 'or blower 28, where it is further compressed and delivered to the cylinders through the intake manifolds 38.

In passing through this system, the air is initially compressed, the heat added to the air by the initial compression is removed by the intercoolers 34, fuel is added to the air by the carburetor 22, the air fuel mixture is further compressed by the blower 28 and is distributed to the cylinders from the blower through the intake manifolds 38.

Most modern aircraft engines are so designed that they develop their maximum permissible horsepower at an altitude considerably above sea level, such engines being commonly designated as altitude rated engines, and being well known to the art. Such an engine may be designed to develop its maximum permissible horsepower at an altitude above sea level of seven thousand, nine thousand or ten thousand feet or any other selected altitude within a reasonable, practical range. In the case of such an engine, a single stage supercharger is obviously more than adequate at altitudes below the rated altitude and when operating below the rated altitude, the engine has to be throttled to prevent it exceeding its permissible horsepower rating. Such engines are very often provided with means for automatically maintaining the pressure of the air in the carburetor air intake substantially constant and at the pressure of the atmosphere at the altitude for which the engine is rated. For a disclosure of such an arrangement, reference may be had to Patent No. 2,082,397 issued May 4, 1937, to Thorp Hiscock for Engine intake regulating means.

The present invention is adapted for application toan engine of the type indicated and the control arrangement is designed to maintain the pressure of the air at the engine air intake substantially constant at the pressure of the selected altitude at all altitudes within the capacity of the multi-stage supercharger.

In order to maintain the pressure of the engine intake air substantially constant, the air supply system is provided with suitable throttling devices and a suitable control is provided for automatically operating the various throttling devices conjointly with each other to provide the desired effect.

The initial throttling device is in the form of a valve 40 comprising a pair of butterfly valve members mounted upon a rotatable shaft 42 extending through the upper part of the intake portion of the casing of the primary supercharger stage 20. The valve 40 is mounted in such position that the butterfly portions thereof are effective to close the lower ends of the ducts 30 where these ducts are led into the intake portion of the primary stage supercharger casing. By means of the valve 40, intake air can be cut off from the primary stage of the supercharger.

A second throttling device takes the form of a valve or a plurality of valves, as indicated at 44, disposed between the intercoolers 34 and the intake portion of the carburetor 22 or, in any case, preferably in proximity to, the air intake of the carburetor. In the illustrated form shown in the drawings, there are two such valves, disposed one upon each side of the carburetor and mounted upon rotatable shafts 46 and 48 extending intake. These valves are effective to control the admission of air to the carburetor. The carburetor also includes the usual throttle valve but a definite disclosure of this valve has been omitted in order to simplify the illustration as the arrangement and operation of such valves are well known to the art.

Each of the ducts 32, leading from the primary supercharger stage tothe carburetor, is provided with an automatic relief valve, as indicated at 50 and particularly illustrated in Fig. 3. Each of .these valves comprises a hinged flap member 52 arranged to cover, from the inside, a reinforced aperture 54 provided in each of the conduits.- Each flap is resiliently urged, by suitable means, such as the spring 56, to the position in which it closes the aperture 54. The spring 56 is made relatively weak so that the flap 52 will move to open the aperture 54, as illustrated in broken lines in Fig. 3, whenever the air pressure within the conduit 32 is slightly less than the air pressure outside of the conduit. 0n the other hand, the flap members 52 will immediately close'the aperture 54 whenever the pressure within the conduit is equal to or slightly above the pressure of the atmosphere outside of the conduit. Thus, when the valve 40 is closed to an extent suflicient to materially restrict the passage of air through the primary stage of the supercharger and reduce the pressure of the air in the conduits 32 below atmospheric pressure, the relief valve 50 will immediately open to admit air from the atmosphere to the carburetor air intake, and when the pressure of the air in the conduits is above that of the surrounding atmosphere the flap valve will close to prevent loss of air from the conduits.

The control device for operating the primary and secondary stage throttling valves to automatically maintain the air pressure in the carburetor air intake substantially constant is schematically illustrated in Fig. 4. The air pressure responsive element of the device comprises a pair of expansible bellows 58 and 60. The bellows 60 is hermetically sealed against the entrance of outside air and the interior of the bellows 58 is connected by means of a suitable conduit 62 with the interior of the carburetor air intake chamber beyond the valve 44. The expansible bellows 60 is evacuated and both bellows are urged towards their expanded condition by included coiled compression springs 64 and 66. This arrangement provides a balance system which is immediately and sensitively responsive to variation of the air pressure within the carburetor air intake chamber. The bellows 58 and 60 are arranged in opposed relation with respect to each other and a lever member 68 is positioned between the two bellows and contacted by the opposed ends of the bellows intermediate its length. This lever is pivotally connected at one end to a fixed support as indicated at and is connected at its opposite end to the stem I2 of a valve controlling a hydraulic servo motor. The pressure responsive device may be adjusted to maintain various selected air pressures in the carburetor air intake chamber by means of a suitable adjusting device generally indicated at 14. For a more detailed description of such an air pressure selecting device reference may be had to application Serial No. 18,430, filed April 26, 1935, by G. E. Beardsley, Jr. and W. A. Parkins for Fuel feeding device for engines, which matured to Patent No.

2,116,876, granted May 10, 1938.

While a particular form of pressure responsive device has been illustrated and described, it is to be understood that various other forms of.pressure responsive devices might be used to control the-servo motor without exceeding the scope of the invention.

The servo motor comprises a cylinder 16 within which are axially slidable stems or shafts l8 and 80 between the adjoining endsof which there is disposed a floating piston 82.

The ends of the cylinder 16 are closed by suitable cap members 84 and 86 which include packing means for the respective stems l8 and 80. The opposite ends of the cylinder 16 are connected by suitable conduits 88 and 80 with the casing 82 of the valve in which the valve element carried by the member 12 operates. The casing 82 is provided with a connection 94 leading to a source of hydraulic fluid under pressure and is provided with two connections 86 and 98 leading to a sump or drain. The pressure connection 94 is led into the mid portion of the casing 92 and the connections 96 and 98 are led into the end portions of the casing.

From the above description, it will be observed that when the valve member 12 is moved to the right as illustrated in Fig. 4, the pressure line 84 will be connected with the conduit 88 to supply fluid under pressure to the right-hand end of the cylinders 16. At the same time, the conduit 90 will be connected with the drain connection 88 permitting fluid to drain out of the lefthand end of the cylinder. The fluid under pressure admitted to the right-hand end of the cylinder will force the piston 82 to the left as viewed in Fig. 4 with a consequent left-hand movement of,

the stem 88. The flange I60 on the stem 18 is provided with peripheral apertures through which the hydraulic fluid may flow so that the stem 18 is not moved. The flange I02 of the stem 86 is similarly constructed.

The stem 80 is pivotally connected by means of a suitable linkage "14 to a lever I06 non-rotatably secured upon the shaft 4'6 or 48 upon which the valve 44 is mounted, the shaft 46 being assumed for the purposeof the illustration. By reason of the connection of the interior of the bellows 'or Sylphon 58 with the interior of the carburetor air intake chamber the bellows will tend to expand upon an increase of the air pressure in the air intake chamber above a predetermined pressure. This expansion of the bellows 58 will move the lever arm 68 to cause a movement of the valve stem 12 to the right with the sequence of events described above. The valve 44 is so arranged that movement of the stem 80 and linkage I04 will tend to close the valve 44 thus restoring the pressure in the carburetor air intake chamber to its normal predetermined value.

When the air pressure in the carburetor air intake chamber falls below the normal predetermined value, the pressure in the interior of the bellows 58 will be reduced and the spring 66 will cause the bellows 60 to expand thereby swinging the lower end of the lever member 68 to the left as viewed in Fig. 4. This movement of the lever member moves the valve stem 12 to the left to connect the pressure line 94 with the conduit 90 leading to the left-hand end of the cylinder I6 and at the same time connects the conduit 88 leading from the right-hand end of the cylinder with the drain connection-86. When the pressure connection 84 is connected with the conduit 80, hydraulic fluid under pressure will be admitted to the left-hand end of the cylinder I6 forcing the piston 82 to the right, thereby permitting the spring I08 to open the valve 44 and admit additional air to the carburetor air intake chamber. When the piston 82 is in its central position with respect to the cylinder 16, as illustrated in Flg. 4, the valve 44 is in its wide open position. Also when the piston 82 is in its central position, as indicated above, or to the right of its central position, the valve of the primary supercharger stage will be in its closed position, the relation of the parts illustrated in Fig. 4 representing the condition of the control when the engine is at the altitude of the maximum capacity of the second- 'ary supercharger stage. If now the pressure of the air in the carburetor air intake chamber remains below the predetermined normal pressure, hydraulic fluid under pressure will continue-to flow into the left-hand end of the cylinder 16 after the piston 82 has reached its central position and the valve 44 has been opened to its widest extent. Further movement of the piston to the right past its central position will move the stem 18 to the right as viewed in Fig. 4 to project the same from the cylinder. The end of the stem I8 is connected by a suitable linkage III! with a lever H2 non-rotatably secured upon the projecting end of the shaft 42 which carries the valve 40 so that movement of the stem 18 to the right will open the valve 40 to render the primary stage of the supercharger efiective to increase the pressure of the carburetor air at altitudes above the critical altitude of the secondary supercharger stage.

When for any reason, such as the descent of the' airplane carrying the engine equipped with the improved control from a high altitude, the pressure in the carburetor intake chamber increases, the valve stem 12 will be moved to the right as viewed in Fig. 4 to connect the conduit 88 with the pressure line 94 and apply fluid under pressure to the right-hand side of the piston 82 thereby forcing the stem to the left. Under these conditions as the piston moves to the left, the valve 40 will first be closed by the action of the spring H4. With continued movement of the piston 82 to the left, the stem 80 will be moved to begin closing the valve 44 in the manner described above. From the above description it will be observed that the pressure in the carburetor air intake chamber is controlled by the valve 44 at altitudes within the controlling capacity of this valve, the valve 4|] of the primary stage of the supercharger remaining closed. As soon,

however, as the range of altitude within which the valve 44 is effective to control the pressure has been exceeded and the valve 44 has been moved to its wide open position, the valve 46 will be actuated to control the pressure by the action of I the primary supercharger stage. within the range at which the valve 44 is effective to control the carburetor pressure, the valve 40 of the primary stage remains closed and the blow er of the primary supercharger stage is rendered ineffective or, its drive may be disconnected if desired by a suitable clutch arrangement either manually or automatically actuated.

Whenever the valve 40 is closed and the air is being supplied to the engine by the secondary blower 28 under the control of the valve, there will be a drop in air pressure between the valve 40 and the valve 44 which will cause the relief valve 50 to open so that air from the surrounding atmosphere will be supplied directly to the carburetor under the pressure control of the valve 44. As soon as the primary stage 26 becomes operative, upon opening of the valve 46, the pressure within the conduit 32 will become greater than At altitudes the pressure of the surrounding atmosphere thereby causing the valve 50 to close and prevent operate in unison by a suitable linkage mechanism generally indicated at I Hi. It is to be understood, however, that a single valve between the carburetor and the conduit 32 may be used without in any way exceeding the scope of the invention.

The carburetor is provided with an easily opened backfire door H8 so that excessive pressures will not be imposed upon the intercoolers 34 in the event of a backfire of the engine. In the illustrative form of the invention shown, this backfire door is located in the bottom wall of the carburetor between the valve parts 44.

The valve or valve parts 44 may obviously be located in any portion of the conduit 32 and the position of the relief valve 50 may also be selected as convenience and efliciency may dictate and a location of the relief valve 50 between the carburetor and intercoolers would in no way exceed the scope of the present invention.

While there has been illustrated and described a suitable mechanical embodiment of what is now considered to be the preferred form of the idea of the invention, it is to be understood that the invention'is not limited to the construction so illustrated and described but that such changes in the size and shape and arrangement of parts may be resorted to as come within the scope of the appended claims.

Having now described the invention so that others skilled in the art may, clearly understand the same what it is desired to secure by Letters Patent is as follows:

What is claimed is:

1. In combination with an aircraft engine having a multi-stage supercharger for supplying air thereto, a duct between the two stages of said supercharger and means for maintaining the air pressure in said duct substantially constant at a preselected value, comprising, a device responsive to the air pressure in said duct, and power actuated means under the control of said pressure responsive means for controlling the various stages of said supercharger in sequence to regulate the air pressure in said duct.

2. A control for a two stage supercharger comprising, means for rendering one stage of said supercharger ineffective and regulating the air pressure developed by the other stage to maintain such pressure substantially constant at a preselected value when said supercharger is operating below a preselected altitude and for rendering said other stage fully operative and regulating the air pressure developed by said one stage to maintain the air pressure substantially constant at said preselected value whenever said supercharger is operating above said preselected altitude.

3. A control for a two stage supercharger having a primary stage and a secondary stage of compression comprising, means for rendering said primary stage ineffective and opening said secondary stage to the atmosphere to cause the same to operate as a single stage compressor whenever the supercharger is operating below a preselected altitude and to render said primary stage effective in cooperation with said secondary stage whenever said supercharger is operating above said preselected altitude, and means for maintaining the pressure of the air delivered by said supercharger substantially constant at a preselected value.

4. A control for a two stage supercharger having a primary stage and a secondary stage of compression and valves between said stages for connecting said secondary stage with the atmosphere, comprising means for rendering said primary stage ineffective and opening said secondary stage to the atmosphere to cause the same to operate as a single stage compressor as long as the atmospheric pressure is above the preselected pressure of the air at the inlet to said secondary stage, and to render said primary stage eifective in cooperation with said secondary stage whenever the atmospheric pressure is below the preselected pressure at the inlet to said secondary supercharger stage, and means associated with both stages of compression of said supercharger and responsive to the pressure of the air at the inlet to said secondary stage to maintain the pressure of the air at the inlet to said secondary stage substantially constant at a preselected value.

5. A control for a two stage supercharger having a primary stage and'a secondary stage of compression and a carburetor pneumatically disposed between said two stages of compression comprising, a valve at the inlet to said carburetor to maintain the pressure in the air intake chamber of said carburetor substantially constant at a preselected value, a valve at the inlet to said primary stage of compression, a valve between said carburetor and said primary stage of compression operative to connect said carburetor with said primary stage of compression or with the external atmosphere depending on whether the pressure of the atmosphere is below or above the pressure of the air at the outlet of said primary stage, and means responsive to the pressure of the air in said carburetor air intake for controlling said valve, said means being effective to maintain the valve at the inlet to said primary stage closed and regulate the pressure in said carburetor by adjusting the valve at said carburetor inlet until said valve at the carburetor inlet reaches its wide open position and to subsequently regulate the pressure in the carburetor air intake by adjusting the valve at the intake to said primary supercharger stage.

6. A control for a two stage supercharger having a primary stage and a secondary stage of compression and a carburetor pneumatically disposed between said two stages comprising, a valve in the air intake to said carburetor, a valve in the air intake to said primary compression stage, and

means responsive to the pressure of the air in said carburetor air intake to maintain said press sure substantially constant at a preselected value byvadjusting-the valve in said carburetor air intake until such valve has been adjusted to its wide open position and by adjusting the valve in the air intake to said primary supercharger stage after the valve in said carburetor air intake has been adjusted to its wide open position.

7. In combination with an aircraft engine and a two stage supercharger therefor, a carburetor pneumatically disposed between the two stages of said supercharger, a valve between said carburetor and the primary stage of said supercharger for regulating the pressure of the air in the carburetor air intake, avalve ahead of the primary stage of said supercharger for regulating the flow of air through said primary supercharger stage, a device responsive to the pressure of the air in said carburetor air intake, a servo mechanism actuated by said pressure responsive device to control said valves, said servo mechanism being effective to open said carburetor air intake valve to its widest extent before starting to open said primary supercharger stage valve and to close said primary supercharger stage valve before beginning to close said carburetor air intake valve.

8. In combination with an aircraft engine and a two stage supercharger therefor, a carburetor pneumatically disposed between the two stages of said supercharger, a valve between said carburetor and the primary stage of said supercharger for regulating the pressure of the air in the carburetor air intake, a valve disposed ahead of the primary stage of said supercharger ior regulating the flow of air therethrough, a device responsive to the pressure of the air in said carburetor air intake, a servo mechanism actuated by said pressure responsive device to control said valve, such servo mechanism being effective to open said carburetor air intake valve to its widest extent before starting to open said primary supercharger stage valve and to close said primary supercharger stage valve before beginning to close said carburetor air intake valve, and a flap valve between said carburetor air intake valve and the external atmosphere to admit air to said carburetor when said primary supercharger stage valve is closed.

9. In combination with an aircraft engine and a two stage supercharger, a carburetor pneumatically disposed between the two stages of said supercharger and connected to said primary supercharger stage by an air duct, a. valve in the air intake of said carburetor for regulating the pressure of the air in the carburetor air intake, a valve in the intake to said primary stage of said supercharger for regulating the flow of air through said primary supercharger stage, a device responsive to the pressure of the air in said carburetor air intake, a servo mechanism actuated by said pressure responsive device to control said valve, said servo mechanism being effective to open said carburetor air intake valve to its widest extent before starting to open said primary supercharger stage valve and to close said primary supercharger stage valve before beginning to open said carburetor air intake valve, and a flap valve in said conduit between said carburetor air intake valve and said primary supercharger stage to admit air to said carburetor from the external atmosphere whenever said primary supercharger stage valve is closed.

10. In combination with an aircraft engine and an engine driven supercharger for compressing the air supplied to said engine, control means at the inlet to said supercharger effective to maintain the pressure of the air in said inlet at a pressure corresponding to a predetermined pressure altitude as long as the pressure of the air at said control means is at or above the pressure corresponding to said predetermined pressure altitude, and an auxiliary supercharger operative at altitudes above the altitude corresponding to said preselected pressure altitude to maintain the pressure of the air at sai control means above the pressure corresponding to said preselected pressure altitude.

WRIGHT A. PARKINS. 

